In Order to Get His Daughter to Start Putting Away

In order to get his daughter to start putting away her school supplies when she gets home from school, Yancy thanks her when she doesn't just drop her backpack in the kitchen upon getting home. After doing this once or twice, he withholds the praise until she takes the backpack to her bedroom. This type of strategy is known as

A) shaping.
B) stimulus generalization.
C) primary reinforcement.
D) stimulus discrimination.